The advent of apparatus for adapting plastic tubing to the standard type of quick-connect sanitary fittings first made available in stainless steel has spurred the growth and popularity of high purity plastic tubing systems. For accommodating rigid tubing to such fittings, U.S. Pat. No. 4,398,879 discloses apparatus for reforming the end of a length of rigid plastic tubing so that the tubing can be adapted in the field to make up with the appropriate standard size of quick-connect sanitary flange fitting. For accommodating flexible hoses to such fittings, patent application Ser. No. 07/915,297 filed Jul. 20, 1992 entitled "Quick-Connect Sanitary Hose Fitting" discloses apparatus for attaching a flexible flange seal to the end of flexible sanitary hose which can be clamped to a stainless steel flange fitting. Another type of fitting for sanitary hoses is shown in U.S. Pat. No. 5,176,411 which discloses a reusable type of sanitary hose coupling. While the availability of suitable couplings for sanitary tubing systems has increased the applicability of such systems, there are applications where a permanent connection of the elements employed in such systems may be required and often the need for making such a permanent connection arises in the field. While ordinary plumbing systems may have their joints cemented together, sanitary systems require that all lumens be smooth and crevice-free. A number of machines have long been known for butt welding thermoplastic pipe sections in a factory setting, such as U.S. Pat. No. 3,022,209 issued Feb. 20, 1962 to Campbell; U.S. Pat. No. 3,276,941 issued Oct. 4, 1966 to Burns; and U.S. Pat. No. 4,075,268 issued Feb. 21, 1978 to Nolan. Heretofore there has been no way conveniently to effect a permanent connection of sanitary tubing elements in the field. In addition, where the work space at the job site is cramped, such as in underground piping systems accessible only through a manhole or in elevated piping systems supported on utility trays, apparatus suitable for use in a factory setting may be too bulky and unwieldy for use at a work site. Additionally, it may be necessary to butt weld variety of different sizes of tubing requiring different temperatures and welding times. Accordingly, a portable apparatus capable of satisfying these desiderata would be a useful tool.
In effecting a butt weld of thermoplastic pipe or tubing it has long been appreciated that a mandrel may be used to maintain the pipe lumen in a clear and smooth condition when the pipe is heated during the welding operation. Examples are shown in U.S. Pat. No. 3,666,586 issued May 30, 1972 to Lacey; U.S. Pat. No. 4,288,266 issued Sep. 8, 1981 to Konrad et al; and U.S. Pat. No. 4,792,374 issued Dec. 20, 1988 to Rianda. The latter patent discloses the use of a pressurizeable bladder made of an elastomeric material such as a silicone or fluorosilicone rubber which is inserted in the bores of the pipe ends to prevent internal beading during the welding operation. However, the use of an elastomeric bladder in contact with the lumen of the heated plastic pipes requires that the air pressure be closely controlled so that the inflated bladder is not over-expanded to distort the pipe lumen and force the heated plastic material to be expressed or flashover at the joint. In addition, the use of an elastomeric bladder that is in intimate contact with the pipe lumen may tend to bind or stick to the walls of the pipes being welded together causing some degree of scarring of the lumen. Maintenance of the smoothness and integrity of the heated pipe lumen becomes even more problematical as the elastomeric material of the bladder tends to retain a set with repeated usage.